proc/setjmp_vars.c

+/* setjmp_vars.c
+
+   Compiling this program with and without optimization yields different
+   results, since the optimizer reorganizes code and variables in a manner
+   that does not take account of the dynamic flow of control established by
+   a long jump.
+
+   Try looking at the assembler source (.s) for the unoptimized (cc -S)
+   and optimized (cc -O -S) versions of this program to see the cause
+   of these differences.
+*/
 #include <stdio.h>
 #include <stdlib.h>
 #include <setjmp.h>
 
 static jmp_buf env;
 
 static void
 doJump(int nvar, int rvar, int vvar)
 {
     printf("Inside doJump(): nvar=%d rvar=%d vvar=%d\n", nvar, rvar, vvar);
     longjmp(env, 1);
 }
 
 int
 main(int argc, char *argv[])
 {
     int nvar;
     register int rvar;          /* Allocated in register if possible */
     volatile int vvar;          /* See text */
 
     nvar = 111;
     rvar = 222;
     vvar = 333;
 
     if (setjmp(env) == 0) {     /* Code executed after setjmp() */
         nvar = 777;
         rvar = 888;
         vvar = 999;
         doJump(nvar, rvar, vvar);
 
     } else {                    /* Code executed after longjmp() */
 
         printf("After longjmp(): nvar=%d rvar=%d vvar=%d\n", nvar, rvar, vvar);
     }
 
     exit(EXIT_SUCCESS);
 }